Many different types of substrate serve as the supporting and interconnecting substrate for electronic components. Resistors, capacitors, inductors, and many other types of electronic component are mounted on the substrate in a predetermined manner and electrically connected together by a metallic conducting pattern that is deposited on its surface to form the required electronic device.
Resistors, capacitors, and other passive components, such as inductors, typically occupy over 50% of the surface area of the substrate. In order to provide more room for active devices (e.g. diodes, transistors, ICs, power sources, etc.) on the surface, as well as to miniaturize the device, multi-layer devices have been constructed. In these devices, electrical circuits consisting of electronic components and conducting patterns are constructed on the substrates that makes up each layer. The layers are electrically connected by via-holes, which are vertical holes that are manufactured through the substrate at the appropriate places to provide conducting paths between the layers.
Many different methods of forming passive electronic circuit elements on substrates have been described. For example:
U.S. Pat. No. 5,855,755 describes the production of passive electronic circuit elements from “electronically conducting polymer films formed from photosensitive formulations of pyrrole and an electron acceptor that have been selectively exposed to UV light, laser light, or electron beams”. The production of the electronic circuit elements requires several steps including periods of thermal treatment or of drying either at room temperature. “Because the photopolymerization process may form lines having sides that are not entirely uniform or smooth, it may be difficult to obtain resistors within narrow tolerances without further processing.” In applications where precise resistance is necessary, the resistor lines are made wider than necessary and, after curing, each of the resistors is measured and trimmed with a laser to increase the resistance. It may be necessary to carry out the trimming process in several stages to achieve the required accuracy.
U.S. Pat. No. 5,872,040 describes a method in which “thin film electronic components are deposited on a surface, parameter values are measured or estimated, a correction offset file is generated, and the components are trimmed using adaptive lithography.” In this example also, many steps are required to produce the electronic components on the substrate and then in the lithography techniques used to trim the films to get the desired electrical values for the elements.
In the currently used methods of producing passive electronic elements, except in the case of parallel plate capacitors in which the substrate itself also serves as the dielectric layer of the capacitor, the elements are produced on one surface of the substrate layers. Thus, creating a multi-layer system results in conducting lines no shorter than the original single layer MCM with the attendant heating, energy loss, and reduced signal to noise ratio.
Most of the existing methods of producing passive elements on substrate surfaces require multi-step, relatively complex, manufacturing processes and relatively large volumes of expensive substrate material. Also, because of the difficulty in controlling the thickness and shape of thin films on the substrate, existing methods result in the production of elements whose electric characteristics vary from their expected values, thus reducing the performance of the device. The accuracy of the components can be improved by trimming them to change their dimensions and therefore their electrical characteristics. This trimming adds to the complexity, time required, and cost of manufacture and sometimes negative results arise such as burning, in the case of laser trimming, or from the harsh chemicals used in lithographic techniques.
U.S. Pat. Nos. 5,953,203 and 6,055,151 disclose methods for producing capacitors on multi-layer ceramic circuit boards, using screen printing techniques, that overcome some of the above mentioned difficulties of the existing methods. In particular, they disclose methods of producing the capacitors that “greatly reduces the shrinkage of the green tapes during firing in the x and y directions, so that most of the shrinkage occurs only in the z, or thickness, dimension”. This, presumably, reduces or eliminates the need for trimming of the capacitors. In addition a method of producing buried capacitors, “buried one or two tape layers below the top of the substrate” is disclosed, reducing somewhat the total surface area of substrate required.
The methods disclosed in these patents only partially alleviate the difficulties of the prior art. They are only applicable to multi-layer circuit boards, and not to other types of substrate. They apply only to the production of capacitors, with restrictions on the capacitance values that are achievable. The method of manufacture is complex requiring the build up of many layers, including barrier layers needed to prevent dilution effects caused by diffusion of material from neighboring layers during fixing of the laminated stacks.
There is therefore a need for providing an improved process for manufacturing electronic components for use on integrated multi-layer MCMs that overcomes the limitations of existing methods.
It is a purpose of this invention to provide a method of manufacturing active and passive electronic components for use on integrated multi-layer MCMs that overcomes the limitations of existing methods.
It is an additional purpose of this invention to provide a method of manufacturing passive electronic components on integrated multi-layer MCMs that is less costly than existing methods. It is a further purpose of this invention to provide a device consisting of integrated multi-layer MCMs that results in reduced module size, shorter conducting lines, reduced power consumption, and improved signal to noise ratio.
Other purposes and advantages of this invention will appear as the description proceeds.